In the 1980's there was a mighty development effort by the automotive companies to replace many metal parts of vehicles with glass fiber reinforced composites (GFRC) to reduce weight and increase gas mileage. Some work was done with thermoplastics, but this was limited due to the extremely high tooling costs incurred for injection molding tooling, and because the viscosity of molten thermoplastics is too high for conventional forming processes used to make large and/or structural GFRC parts, such processes as RIM (Reactive Injection Molding), SRIM (Structural Reactive Injection Molding), RTM (Resin Transfer Molding), VARTM (Vacuum Assisted Resin Transfer Molding), SMC (Sheet Molding Compound), BMC (Bulk Molding Compound), spray-up forming, filament winding, LFI (Long Fiber Injection molding) and pultrusion, much work was being done on thermoset GFRC. In the injection molding process chopped glass fibers and pellets of a thermoplastic polymeric resin are fed into an extruder mix the two together at elevated temperature and maceration due to the high viscosity of the molten thermoplastic polymer(s) or copolymer(s). Substantial working and maceration is important and sometimes necessary to wet out the glass fibers at the elevated temperature due to the high viscosity, and as a result the glass fibers are shortened significantly. The resultant mixture is formed into a molding material that is supplied to a press or injection molding system to be formed with very expensive tooling into GFRC parts. During the extrusion process using single or twin-screw machines, the resin is melted and the fibres are dispersed throughout the molten resin to form a fibre/resin mixture. Next, the fibre/resin mixture may be degassed, cooled, and formed into pellets. The dry fibre strand/resin dispersion pellets are then fed to a moulding machine and formed into moulded composite articles that have a substantially homogeneous dispersion of glass fibre strands throughout the composite article. Alternatively, in the process using continuous filaments, fibreglass filaments are mixed with the molten resin in an extruder with the screw geometry designed to mix the matrix with fibres without causing significant damage to the fibres. The resultant extruded mixtures are then compression molded to form long-fibre reinforced thermoplastic parts having superior mechanical properties due to the nature of the orientation and the longer length of the fibers. Because of these difficulties, the use of thermoplastics to make vehicle parts was very limited.
Therefore, much development work was being done and products were being commercialized using thermoset polymer chemistry and materials to make GFRC. Much of this work came to naught because of recycling advantages of metal parts versus thermoset GFRC parts. Metal parts can be remelted at a cost advantage versus melt from iron ore, making scrap metal valuable, but thermoset GFRC parts are not recyclable and no valuable use for scrap thermoset GFRC parts could be found. Consequently, if a significant portion of vehicles were to be made of thermoset GFRC, huge piles of worthless and useless scrap would result along with unfavourable economics. Consequently, further GFRC penetration of the automotive market slowed to almost a standstill, and even regressed in some applications.
With the newly proposed challenging CAFE gas mileage standards just introduced, there is a larger than ever need for lighter weight vehicle parts which thermoplastic GFRC could satisfy, because thermoplastic GFRC scrap is recyclable. The thermoplastic polymers or copolymers can be melted and reclaimed and ground thermoplastic GFRC can be used in conventional thermoplastic forming processes including injection molding, extrusion, etc. Thus, there is a larger than ever need to be able to make thermoplastic GFRC parts using thermoset processes including RIM, SRIM, RTM, VARTM, LFI, SMC, BMC, etc.
It is known to cast low viscosity caprolactam monomers, one containing an activator and another mixture containing a caprolactam monomer and a catalyst by mixing the two very low viscosity mixtures together prior to casting. This mixture must be kept to less than about 100 degrees C. to prevent rapid polymerization, then, following casting, the cast mixture is heated in the mold to cause anionic polymerization of the monomer to produce a polyamide, but this method is not practical for most vehicle parts and many other current thermoset parts. If thermoplastic GFRC is to replace metals substantially in the automotive industry and elsewhere, economical method(s) must be found that will produce such automotive parts of equal or superior performance at competitive costs with metals. This is achieved with the methods of the invention.